This invention relates to closures, and more particularly, to a composite plastic closure for bottles.
Over the years metal crowns have been lined with various materials such as cork, rubber, thermosetting plastic and thermoplastic. Representative of the many crowns lined with such material are those shown in U.S. Pat. Nos. 1,486,937, 2,548,305, 2,654,913, 2,684,774, 2,688,776, 2,696,318, 2,823,422, 2,834,498, 2,840,858, 2,952,035, 3,183,144, 3,278,985 and 3,300,072. These prior art crowns have met with varying degrees of success.
Recently, the advantages of plastic crowns and closures have been recognized. The physical characteristics and nature of plastics, however, such as their melting and plastic deformation temperatures, and their resiliency, impact and compression strengths, at molding and refrigeration temperatures, present different structural problems in molding plastic closures than in metal closures.
In prior art plastic closures, for example, the wall thickness is confined to a limited range, i.e., the wall must be thin enough to permit axial removal and deflection of the threaded skirt of the closure from the plunger, but thick enough to support the necessary thread height and profile. The threads of conventional plastic closures are also limited to a certain amount of taper to permit deflection and removal of the threaded skirt from the plunger.
In conventional plastic closures, such as polypropylene closures, the closures have low impact strength and fail a drop test in the refrigeration range of 32-40 degrees F.
It is therefore desirable to provide an improved plastic closure which overcomes most, if not all, of the above disadvantages.